Image forming apparatus

ABSTRACT

An image forming apparatus includes a photosensitive member; a developing device for developing an electrostatic image formed on said photosensitive member into a toner image; a transfer charger for transferring a toner image from said photosensitive member onto an image receiving member; a non-rotational brush and a rotatable brush for electrically charging toner, which remains on said photosensitive member after image transfer by said transfer charger, to collect the remaining toner into said developing device; a driving mechanism provided with a driving source for rotating said rotatable brush; and a moving mechanism for reciprocating said non-rotational brush by a driving force through said rotatable brush in a direction along an axis of said photosensitive member.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image forming apparatus such as acopying machine, a printer, a facsimile machine, or a multi-functionmachine having a plurality of functions of these machines.

In an image forming apparatus for effecting image formation by using anelectrophotographic process, untransferred toner on a photosensitivemember has been conventionally removed and collected by a cleaner. Onthe other hand, an image forming apparatus employing a so-calledcleanerless system in which the untransferred toner on thephotosensitive member is collected in a developing device withoutproviding such a cleaner has been commercially available.

In such an image forming apparatus employing the cleanerless system, ithas been practiced that the untransferred toner on the photosensitivemember is electrically charged to enhance a collecting efficiency in thedeveloping device. Specifically, in an apparatus disclosed in JapaneseLaid-Open Patent Application (JP-A) 2003-167477, a constitution in whichtwo non-rotational brushes are disposed in contact with thephotosensitive member and are used to electrically charge theuntransferred toner on the photosensitive member is employed.

In an apparatus described in JP-A 2003-167477, a mechanism forreciprocating the non-rotational brushes in an axial (shaft) directionof the photosensitive member (a so-called reciprocating mechanism) isprovided in order to properly perform charging of the untransferredtoner on the photosensitive member by the brushes. By employing such amechanism for reciprocating the non-rotational brushes, it is possibleto disperse the untransferred toner in a rotation axis direction of thephotosensitive member. Therefore, it is possible to suppress localaccumulation of the untransferred toner in an area of a part of thenon-rotational brushes and thus to properly perform the charging of theuntransferred toner. As a result, it is possible to enhance thecollecting efficiency of the untransferred toner in the developingdevice.

In an apparatus described in JP-A 2005-234035, the collecting efficiencyof the untransferred toner is further enhanced by using a non-rotationalbrush and a rotatable brush.

However, in the apparatus using the non-rotational brush and therotatable brush as described in JP-A 2005-234035, in the case where thecollecting efficiency of the untransferred toner in the developingdevice is intended to be further enhanced by reciprocating thenon-rotational brush as in the apparatus described in JP-A 2003-167477,there is a possibility that an increase in cost occurs.

That is, in the case of providing a driving source exclusively forreciprocating the non-rotational brush in the axial direction inaddition to a driving source for rotating the rotatable brush, itresults in the increase in cost.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide an imageheating apparatus capable of properly performing charging ofuntransferred toner without providing a driving source exclusively forreciprocating a non-rotational brush in an axial direction in additionto a driving source for rotating a rotatable brush.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an image forming apparatusincluding a cleanerless system.

FIG. 2 is a schematic sectional view showing a driving mechanism for aphotosensitive member, a non-rotational brush, and a rotatable brush.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed.

FIG. 1 is a sectional view of a cleaner-less color printer (imageforming apparatus), and shows the general structure of the printer. Thiscolor printer is structured to form a color image with the use of anelectrophotographic process. First, the image forming portion of thecolor printer will be described.

(Image Forming Portion)

Referring to FIG. 1, the image forming apparatus in this embodiment isprovided with four image formation stations (A, B, C, and D) as theimage forming portions of the apparatus. The four image formationstations are the same in structure. Hereafter, therefore, only the imageformation station A will be described in detail; the other imageformation stations will not be described in detail. In terms of rolesand functions, the image formation stations A, B, C, and D form imageswith the use of yellow, magenta, cyan, and black toners, respectively.

The image formation station A has a photosensitive member 11 a as animage bearing member. The photosensitive member 11 a is rotatable in thedirection indicated by an arrow mark in the drawing. It is rotationallydriven by a motor 62 a (FIG. 2), which is the driving force source thatfunctions as a part of the mechanism for driving the photosensitivemember 11 a. In this embodiment, an organic photosensitive member (OHP)is used as the photosensitive member 11 a. In terms of the directionparallel to the axial line of the photosensitive member 11 a, the areaof the peripheral surface of the photosensitive member 11 a, acrosswhich an image can be formed, is slightly wider than the dimension of arecording sheet P of A4 size, in its lengthwise direction.

The color printer is provided with a charging device 12 a, an exposingapparatus 23 a, a developing device 13 a, a charging device 14 a forfirst image transfer, and a pair of auxiliary charging devices 15 a and16 a, which are disposed in the adjacencies of the peripheral surface ofthe photosensitive member 11 a, in the listed order in terms of therotational direction of the photosensitive member 11 a. The auxiliarycharging device 15 a is in the form of a rotational brush, whereas theauxiliary charging device 16 a is the form of a non-rotational bush.

As a print command reaches the color printer from an external hostcomputer through network cables, the photosensitive member 11 a beginsrotate. Then, the peripheral surface of the photosensitive member 11 ais uniformly charged to the negative polarity (which is −600 V in thisembodiment) by the charging device 12 a. The charging device 12 a inthis embodiment is in the form of a charge roller. It contains anelectrically conductive substance (ion-conductive substance) by such anamount that makes the electrical resistance (at normal temperature andnormal humidity) of the charge roller 12 a fall in a range of 10⁵-10⁷Ω.When charging the photosensitive member 11 a, a charge bias, which is acombination of DC and AC voltages, is applied to the charge roller 12 a.The charge bias in this embodiment is a combination of a DC voltage of−600 V, and an AC voltage which is 2 KHz in frequency and 1.5 KV inpeak-to-peak voltage.

Then, a beam of laser light is projected upon the peripheral surface ofthe photosensitive member 11 a by an exposing apparatus 23 a, whilebeing modulated with the image formation data inputted from the hostcomputer. As a result, an electrostatic image, which reflects the imageformation data, is formed on the peripheral surface of thephotosensitive member 11 a. The image formation data are inputted intothe printer when the aforementioned print command is inputted.

Then, the electrostatic image formed on the photosensitive member 11 aas described above is made visible by the developing device 13 a, whichuses yellow toner. During this process, a development bias (which is−300 V of DC voltage in this embodiment) is applied to the developmentroller of the developing device 13 a from a high voltage source. In thecase of the development method used in this embodiment, the normalpolarity to which the photosensitive member 11 a is charged, and thenormal polarity to which the toner is charged, are both negative, thatis, being the same in polarity. In other words, the image formingapparatus in this embodiment uses a so-called reverse developmentmethod. Incidentally, a combination of a DC voltage and an AC voltagemay be applied as the development bias, in order to improve theapparatus in development efficiency. The amount of charge given to theyellow toner stored in the developing device is in a range of −25-−36μC/mg. Further, in order to adjust the yellow toner in fluidity, suchsilica that is 20 nm in particle diameter and has been treated with oilhas been added to the yellow toner. The ratio by which the silica isadded is no more than 30%.

Then, the yellow toner image formed on the photosensitive member 11 a istransferred (first transfer) onto an intermediary transfer belt 21(transfer medium) by the first transfer charging device 14 a (transfercharger). For this transfer, a first transfer bias (+500 V in thisembodiment) is continuously applied to the first transfer charger 14 a,which is the form of a roller (transfer roller) in this embodiment.

After the completion of the first transfer, the toner remaining on thephotosensitive member 11 a (which hereafter will be referred to astransfer residual toner), that is, the toner having failed to betransferred onto the intermediary transfer belt 12 from thephotosensitive member 11 a, is charged by the non-rotational brush 16 a,and then, by the rotational brush 15 a, as will be described later.

As the charged transfer residual toner reaches where it faces thedeveloping device 13 a, it is electrostatically recovered by thedeveloping device 13 a. For the recovery of the transfer residual toner,the development bias is applied to the development roller of thedeveloping device 13 a. In the case of a job in which two or more imagesare continuously formed, the electrostatic images are formed on thephotosensitive member 11 a while the transfer residual toner isrecovered from the photosensitive member 11 a by the developing device13 a. That is, the above described development process and transferresidual toner recovery process are simultaneously carried out.

Described above is the image formation sequence carried out in each ofthe image formation stations.

The intermediary transfer belt 21, onto which a visible image formed ineach image formation station is transferred, is below the imageformation stations A-D. It is suspended, and remains stretched, by theintermediary transfer belt rollers 17-19. It is circularly driven in thedirection indicated by an arrow mark in the drawing, by the intermediarytransfer belt roller 17, which also functions as the belt drivingroller. The intermediary transfer belt 21 is formed of PI (polyimide)resin. It is 5 μm in thickness, and its volume resistivity is in a rangeof 10⁹-10¹⁰ Ω×cm.

An image formation process, which is similar to the above described one,is carried out in each of the other image formation stations B-D. Then,the four toner images formed in the image formation stations A-D, onefor one, are sequentially transferred in layers (first transfer) ontothe intermediary transfer belt 21, forming thereby a full-color tonerimage on the intermediary transfer belt 21.

After being formed as described above, the four monochromatic tonerimages of the full-color toner image are transferred together (secondtransfer) by the second transfer charging device 20, onto a sheet P,which is a sheet of recording medium. For this transfer, a secondtransfer bias (which is +1000 V in this embodiment) is applied to thetransfer roller, which is the second transfer charging device 20. Afterthe second transfer, the toner remaining on the intermediary transferbelt 21 is removed by a cleaner 24, and is recovered by the cleaner 24,to be used for the following image formation.

Thereafter, the full-color image formed on the sheet P is fixed to thesheet P by being heated and pressed by a fixing apparatus 22. Afterbeing subjected to the fixing operation, the sheet P is discharged fromthe image forming apparatus, ending the image formation.

(Cleaner-Less System for Cleaning Photosensitive Drum)

Next, the photosensitive drum cleaning system in this embodiment will bedescribed, which does not have a cleaner dedicated to the cleaning ofthe photosensitive drum. Since the four photosensitive drum cleaningsystems employed by the four image formation stations A-D, one for one,are identical. Therefore, only the cleaner-less photosensitive drumcleaning system of the image formation station A will be described indetail; the cleaner-less photosensitive drum cleaning systems in otherimage formation stations will not be described.

The transfer residual toner, that is, the toner which failed to betransferred (first transfer) from the photosensitive member 11 a by thefirst transfer charging device 14 a and is remaining on thephotosensitive member 11 a, is charged, first, by the non-rotationalbrush 16 a (auxiliary charging device), and then, is charged by therotational brush 15 a (auxiliary charging device). The non-rotationalbrush 16 a and rotational brush 15 a, which are the auxiliary chargingdevices, are kept within a cover 100 a for the auxiliary chargingdevices, which is roughly U-shaped in cross section (FIG. 1).

In terms of the charging the transfer residual toner, the rotationalbrush 15 a is higher in performance than the non-rotational brush 16. Inthis embodiment, therefore, in order to properly charge the transferresidual toner, the rotational brush 15 a is used as the secondauxiliary charging device for charging the transfer residual toner.

Hereafter, the non-rotational brush 16 a and rotational brush 15 a willbe described in detail.

(Non-Rotational Brush)

The non-rotational brush 16 a in this embodiment is a so-called deckbrush, which is made up of a supporting board, and nylon fibers. Thenylon fibers are 6 denier in thickness, 5 mm in length, and 100 KF indensity. The nylon fibers contain the carbon dispersed therein as anelectrical resistance adjustment agent; the volume resistivity of thenylon fibers has been adjusted to be in a range of 10⁵-10⁶ Ω×cm. By theway, the nylon fiber to be used as the material for the non-rotationalbrush 16 a may be a nylon fiber, the electrical resistance of which hasbeen adjusted by coating the fiber with carbon.

The non-rotational brush 16 a is fixed to the holder 16A, which isroughly U-shaped in cross section. The holder 16A is attached to thecover 100 a for the auxiliary charging devices (non-rotational androtational brushes 16 a and 15 a) so that the holder 16A is not allowedto rotate, and also, so that the fiber portion of the non-rotationalbrush 16 a remains in contact with the photosensitive member 11 a. Thatis, the relationship between the non-rotational brush 16 a andphotosensitive member 11 a is such that as the photosensitive member 11a is rotated, the non-rotational brush 16 a rubs the peripheral surfaceof the photosensitive member 11 a (while charging transfer residualtoner). Further, the holder 16A is supported by a shaft attached to thecover 100 a so that the holder 16A is allowed to move back and forth inthe direction parallel to the rotational axis of the photosensitivemember 11 a while holding the non-rotational brush 16 a, as will bedescribed later.

By the way, the material for the non-rotational brush 16 a may bepolyester fibers. Further, the fibers are desired to be 2-10 denier inthickness, 3-8 mm in length, and 50-500 KF in pile density.

The fiber supporting plate of the non-rotational brush 16 a is inconnection with a high voltage power source, which is for applying tothe non-rotational brush 16 a, a charge bias (first auxiliary chargebias) which is opposite in polarity to the normal polarity to which thetoners are charged. In this embodiment, +600 V of DC voltage is appliedas the first auxiliary charge bias. Further, for reliability, an ACvoltage (which is 400 V in peak-to-peak voltage, for example) may beapplied in combination with the DC voltage.

(Rotational Brush)

The rotational brush 15 a in this embodiment is made up of a piece ofpile formed of nylon fiber, and an electrically conductive base to whichthe pile is planted. The nylon fibers are 6 denier in thickness, and are10 mm in length. The pile is 100 KF in fiber density. The electricallyconductive base is attached to a hollow metallic core, which isrotatably supported. That is, the rotational brush 15 a is in the formof a roller.

In this embodiment, the rotational brush 15 a is rotationally disposedso that its fibrous portion remains in contact with the photosensitivemember 11 a. By the way, the material for the rotational brush 15 a maybe polyester fiber. If the polyester fiber is used as the brushmaterial, it is desired to be 2-10 denier in thickness, 5-10 mm inlength, and the fiber density is desired to be in a range of 50-500 KF.Further, this nylon fiber contains carbon dispersed therein aselectrical resistance adjustment agent; the volumetric resistivity ofthe fiber has been set to be in a range of 10⁵-10⁶ Ω×cm. By the way, thenylon fiber to be used as the material for the rotational brush 15 a maybe a nylon fiber, the electrical resistance of which has been adjustedby coating the surface of the fiber with carbon.

The metallic core portion of the rotational brush 15 a is in connectionto a high voltage power source so that the second auxiliary charge bias,which is the same in polarity as the normal polarity of the toners, isapplied to the metallic core portion. In this embodiment −1000 V of DCvoltage is applied as the second auxiliary charge bias.

Next, the reason why the above described cleaner-less photosensitivedrum cleaning system was employed in this embodiment will be described.

The transfer residual toner on the photosensitive member 11 a, that is,the toner having failed to be transferred (first transfer) and remainingon the photosensitive member 11 a, contains two kinds of toner, that is,the normally charged toner (negatively charged toner) and the so-calledreversal toner (positively charged toner), or the toner which isopposite in polarity from the normally charged toner.

In order to electrostatically and efficiently recover the transferresidual toner on the photosensitive member 11 a, into the developingdevice 13 a, it is required to make all the transfer residual tonernormal (negative) in polarity, and roughly the same (−25-35 μC/mg) inthe amount of charge. On the other hand, in order to charge the transferresidual toner so that all the transfer residual toner becomes normal inpolarity, and has a preset amount of charge, it is desired to charge(first auxiliary charging process) the transfer residual toner to thereverse polarity (positive polarity) before charging the transferresidual toner to the negative polarity.

In this embodiment, therefore, the bias which is opposite in polarity tothe normal bias applied to the charging device is applied to thenon-rotational brush 16 a, whereas the bias which is the same (negative)in polarity as the normal bias applied to the charging device is appliedto the rotational brush 15 a.

Further, the secondary auxiliary charge bias is set so that thepotential level to which the photosensitive member 11 a is charged bythe application of the auxiliary charge bias (−1000 V) will be smallerin absolute value than the potential level to which the photosensitivemember 11 a is charged by the application of the bias (−600 V) to thecharging device 12 a. This setting is for preventing the problem thatafter the transfer residual toner is negatively charged by therotational brush 15 a, it electrostatically transfers onto the chargingdevice 12 a when the photosensitive member 11 a is charged by thecharging device 12 a.

The above described charging of the transfer residual toner, andrecovery of the transfer residual toner recovery into the developingdevice, are also carried out in the other image formation stations B-D.

(Driving Mechanism)

Next, referring to FIG. 2, the driving mechanism for rotationallydriving the rotational brush 15 a will be described. Since the fourrotational brush driving mechanisms employed by the four image formationstations, one for one, are the same in mechanism, only the rotationalbrush driving mechanism of the image formation station A will bedescribed in detail; the other rotational brush driving mechanisms willnot be described.

In this embodiment, the photosensitive drum cleaning system is notstructured to directly input driving force to the rotational brush 15 afrom a driving force source. Instead, it is structured so that therotational brush 15 a receives rotational driving force from the drivingforce source by way of the photosensitive member 11 a. Morespecifically, the image forming apparatus in this embodiment isstructured so that the photosensitive member 11 a and rotational brush15 a share a single driving force source. Not only can this setup reducethe apparatus in cost, but also, in size.

More concretely, the driving force transmission mechanism forrotationally driving the photosensitive member 11 a is structured asfollows. The driving force transmission mechanism has: a motor 62 a as adriving force source; and a coupling 62 a attached to the drive shaft ofthe motor 62 a.

The one end of the rotational axle of the photosensitive member 11 a isprovided with a flange 80 a, which has a coupling 70 a. The imageforming apparatus is structured so that this coupling 70 a isconnectible to the aforementioned coupling 61A to transmit therotational driving force from the motor 62 a to the photosensitivemember 11 a. Thus, as the motor 62 a is activated by the CPU as acontroller, the photosensitive member 11 a rotates at a presetperipheral velocity in the direction indicated by an arrow mark in thedrawing.

Further, in this embodiment, the image forming apparatus is providedwith a mechanical linkage for driving the rotational brush 15 a with theuse of the driving force that drives the photosensitive member 11 a.More concretely, the mechanical linkage has an driving force output gear71 a, which is attached to a flange 81 a, which is attached to theopposite end of the photosensitive member 11 a from the coupling 70 a interms of the axial direction of the photosensitive member 11 a. Themechanism linkage has also a driving force input gear 85 a, with whichthe rotational axle of the rotational brush 15 a is provided. Thisdriving force input gear 85 a is in engagement with the driving forceoutput gear 71 a.

The rotational brush 15 a is rotationally borne at its lengthwise endportions, by the cover 100 a for the auxiliary charging devices.Further, the rotational brush 15 a is held to the cover 100 a to make itvirtually impossible for the rotational brush 15 a to move in itslengthwise direction.

In other words, the image forming apparatus is structured so that therotational brush 15 a is rotated by the rotational force transmitted tothe rotational brush 15 a by way of the photosensitive member 11 a.Further, the rotational brush 15 a is connected to the photosensitivemember 11 a through the gear 85 a and 71 a so that the peripheralsurface of the rotational brush 15 a moves in the same direction as theperipheral surface of the photosensitive member 11 a, in the area ofcontact (charging area) between the peripheral surface of the rotationalbrush 15 a and the peripheral surface of the photosensitive member 11 a.Further, the gear ratio between the gears 71 a and 85 a is set so thatthe rotational brush 15 a rotates at a peripheral velocity which ishigher than the peripheral velocity of the photosensitive member 11 a.In other words, the following phenomenon has been taken intoconsideration. That is, when the tip portion of each fiber of therotational brush 15 a leaves the photosensitive member 11 a, it is madeto flip away from the photosensitive member 11 a, by its own resiliency,and therefore, the transfer residual toner in the rotational brush 15 ais spitted out toward the photosensitive member 11 a. Thus, this setupmakes it possible to prevent the problem that the amount by which thetransfer residual toner remains in the rotational brush 15 a after beingtaken into the rotational brush 15 a increases.

The rotational brush driving mechanisms in the other image formationstations B-D are the same as the rotational brush driving mechanism inthe image formation station A, which was described above. That is, theyalso are structured so that rotational brushes 15 b-15 d charge (secondauxiliary charge) the transfer residual toner on the photosensitivemembers 11 b-11 d, respectively, while rotating, as does the rotationalbrush 15 a.

(Brush Reciprocating Mechanism)

Next, referring to FIG. 2, the mechanism for reciprocally moving thenon-rotational brush 16 a in the direction parallel to rotational axisthe photosensitive member 11 a will be described. Since the four imageformation stations are the same in the mechanism for reciprocally movingtheir non-rotational brushes 16, only the mechanism in the imageformation station A will be described in detail; those in the otherimage formation stations will not be described.

In order to deal with such a situation that in terms of the directionparallel to the rotational axis of the photosensitive member 11 a, someportions of the peripheral surface of the photosensitive member 11 acollect more transfer residual toner than the other, the image formingapparatus in this embodiment is structured so that the non-rotationalbrush 16 a can be reciprocally moved in the direction parallel to theaxial line of the photosensitive member 11 a. The employment of amechanism for reciprocally moving the non-rotational brush 16 a makes itpossible to disperse the transfer residual toner on the photosensitivemember 11 a, in the direction parallel to the axial line of thephotosensitive member 11 a. In other words, the employment makes itpossible to prevent the transfer residual toner from unevenlyaccumulating in the rotational brush 15 a in terms of the directionparallel to the axial line of the rotational brush 15 a. Therefore, theemployment of this mechanism for reciprocally moving the non-rotationalbrush 16 a makes it possible to keep the rotational brush 15 a as highas possible in its charging performance (second auxiliary charge), whichin turn makes it possible keep as high as possible the efficiency withwhich the transfer residual toner is recovered from the photosensitivemember 11 a into the developing device 13 a. Therefore, it becomespossible for the photosensitive member 11 a to be properly charged bythe charging device 12 a; it becomes possible to charge thephotosensitive member 11 a at a highest level of uniformity in potentiallevel, in terms of the lengthwise direction of the photosensitive member11 a.

In this embodiment, the mechanism for reciprocally moving thenon-rotational brush 16 a is not provided with a driving force sourcededicated to the non-rotational brush 16 a. Instead, the image formingapparatus is structured so that the driving force from the motor 62 a isused for reciprocally moving the non-rotational brush 16 a. That is, thestructural arrangement employed in this embodiment for reciprocallymoving the non-rotational brush 16 a is such that the driving forceinputted into the photosensitive member 11 a from the motor 62 a isoutputted to the rotational brush 15 a, and then, the driving forceinputted into the rotational brush 15 a is inputted into thenon-rotational brush 16 a. That is, the driving force for rotating thephotosensitive member 11 a is also used as the driving force source forreciprocally moving the non-rotational brush 16 a. In other words, notonly can the present invention reduce an electrophotographic imageforming apparatus in cost, but also, in size.

More concretely, the rotational shaft of the rotational brush 15 a isprovided with a cam 83 a (groove) in addition to the driving force inputgear 85 a. Thus, as the rotational driving force from the motor 62 a isinputted into the rotational brush 15 a by way of the photosensitivemember 11 a, the cam 83 a rotates with the rotational brush 15 a.

The holder 16A, which holds the non-rotational brush 16 a, is providedwith a pair of shafts, which extend from the lengthwise ends of theholder 16A, one for one, in the direction parallel to the axial line ofthe holder 16A. Further, the end portion of one of the two shafts of theholder 16A is provided with a boss 84 a, which is in engagement with thecam 83 a (groove) of the rotational brush 15 a. The two shafts of theholder 16A are borne by the cover 100 a of the auxiliary chargingdevices in such a manner that they can be reciprocally moved together.Therefore, the non-rotational brush 16 a is reciprocally moved by thedriving force inputted into the non-rotational brush 16 a from the motor62 a by way of the photosensitive member 11 a and rotational brush 15 a.The two ranges indicated by two referential letters W are the ranges inwhich the lengthwise ends of the non-rotational brush 16 a reciprocallymove, respectively. In terms of the lengthwise direction of thephotosensitive member 11 a, the range across which the non-rotationalbrush 16 a is enabled to contact the peripheral surface of thephotosensitive member 11 a is slightly wider than the area of thephotosensitive member 11 a, across which an image can be formed. Thereciprocal range W of the non-rotational brush 16 a can be adjusted bychanging the angle of the cam 83 a.

In terms of the above described mechanism for reciprocally moving thenon-rotational brush, the other image formation stations B-D are thesame as the image formation station A. That is, the other imageformation stations B-D are structured so that the non-rotational brushes16 b-16 d charge the photosensitive members 11 b-11 d, respectively,while reciprocally moving, as does the non-rotational brush 16 a.

This embodiment of the present invention makes it possible to reduce enelectrophotographic image forming apparatus in cost and size, and also,to simplify the image forming apparatus in structure, by employing theabove described driving force inputting mechanism for reciprocallymoving the non-rotational brush 16.

(Verification)

Next, the results of the verification of this preferred embodiment ofthe present invention, which was obtained by continuously forming 1,000prints, using the sheets P of A4 size, will be described.

More specifically, identical prints, which are high in image densityacross a certain range in terms of the direction parallel to therotational axis of the photosensitive member 11 a (identical prints ofimage having long stripe which is 5 cm wide in terms of lengthwisedirection of photosensitive member) were continuously formed.

Since the image forming apparatus in this embodiment was structured sothat the transfer residual toner was dispersed in the direction parallelto the rotational axis of the photosensitive member, the problem thatthe transfer residual toner is not recovered into the developing device,did not occur even at the end of the printing operation in which 1,000identical prints was made using the sheets P of A4 size.

On the other hand, in the case of a comparative image forming apparatus,which was not structured to reciprocally move the non-rotational brush,it was impossible for the transfer residual toner to be dispersed in thedirection parallel to the rotational axis of the photosensitive member.Thus, the phenomenon that the transfer residual toner fails to berecovered into the developing device began to occur when roughly the100th print was made using the sheets P of A4 size. Some transferresidual toner transferred onto the sheet P, which resulted in theformation of unsatisfactory images.

That is, the effect of reciprocally moving the non-rotational brush wasconfirmed.

In the case of the image forming apparatus in the above describedpreferred embodiment of the present invention, the rotational brushes 15a-15 d are not reciprocally moved in the direction parallel to therotational axes of the photosensitive members 11 a-11 d, respectively,for the following reason.

That is, the non-rotational brush in this embodiment bears the role ofthe first auxiliary charging device for charging the transfer residualtoner. Therefore, even if the non-rotational bush unsatisfactorilycharges the transfer residual toner because of the flattening of itspile, there is not going to be a large problem, because, in order tocompensate for the incomplete charging of the transfer residual toner bythe non-rotational brush, the image forming apparatus is structured sothat after the transfer residual toner is charged (first auxiliarycharge) by the non-rotational brush, it is charged (second auxiliarycharge) again by the rotational brush.

On the other hand, the rotational brush bears the role of carrying outthe final process of charging the transfer residual toner. Therefore, ifit fails to satisfactorily charge the transfer residual toner because ofthe flattening of its fibrous pile, the transfer residual toner is notgoing to be satisfactorily recovered. In other words, there is directconnection between the unsatisfactory charging of the transfer residualtoner by the rotational brush and the unsatisfactory recovery of thetransfer residual toner.

Further, if the image forming apparatus in this embodiment is structuredso that the rotational brush also is reciprocally moved, it is possiblethat the rotational brush will be deformed in a manner to negativelyaffect the charging performance of the rotational brush. Thus, thestructural arrangement for reciprocally moving the rotational brush isnot employed in this embodiment. Therefore, the moment the tip of eachfiber of the rotational brush separates from the photosensitive drum, itflips up, and as it flips up it flings the transfer residual toner backonto the photosensitive drum. Further, it is reasonable to think thatthis effect will last for a long time.

As described above, the present invention makes it possible to structurean electrophotographic image forming apparatus so that thenon-rotational brush of the apparatus is reciprocally moved withoutproviding the apparatus with a driving force source dedicated to thereciprocal movement of the rotational brush. Thus, the present inventionmakes it possible to reduce an electrophotographic image formingapparatus in cost and size, and also, to simplify the apparatus.

In the preferred embodiment described above, a single driving forcesource was shared by the photosensitive drum and rotational brush. Thissetup, however, is not mandatory. For example, the photosensitive drumand rotational brush may be provided with their own driving powersource, and the non-rotational bush may be reciprocally moved using thedriving force which is directly inputted into the rotational brush fromthe driving force source dedicated to the rotational brush. From thestandpoint of reducing an electrophotographic image forming apparatus incost and size, and simplifying the apparatus, the structural setup inthe preferred embodiment is preferable.

Further, in the preferred embodiment, a cam was used to convert therotational force from the rotational brush, into the force forreciprocally move the non-rotational brush. However, this setup is notmandatory. That is, any of known mechanisms capable of making the sameconversion as that in this preferred embodiment may be employed.

In the preferred embodiment, a toner image formed in each of the imageformation stations was transferred onto the intermediary transfer belt(first transfer), and then, is transferred (second transfer) from theintermediary transfer belt onto a sheet of recording medium. However,this setup is not mandatory for the application of the presentinvention.

For example, the present invention is also applicable to anelectrophotographic image forming apparatus which is provided with arecording medium conveying belt, instead of the intermediary transferbelt, and in which a toner image formed in each of the image formationstations is directly transferred onto the sheet of recording mediumbeing conveyed by the recording medium conveying belt. In this case, thesheet of recording medium functions as only recording medium to which animage is transferred.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth, and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application No.262995/2008 filed Oct. 9, 2008 which is hereby incorporated byreference.

1. An image forming apparatus, comprising: a photosensitive member; adeveloping device for developing an electrostatic image formed on saidphotosensitive member into a toner image; a transfer charger fortransferring a toner image from said photosensitive member onto an imagereceiving member; a non-rotational brush and a rotatable brush forelectrically charging toner, which remains on said photosensitive memberafter image transfer by said transfer charger, to collect the remainingtoner into said developing device; a driving mechanism provided with adriving source for rotating said rotatable brush; and a moving mechanismfor reciprocating said non-rotational brush by a driving force throughsaid rotatable brush in a direction along an axis of said photosensitivemember.
 2. An apparatus according to claim 1, wherein said movingmechanism includes a cam portion provided on a shaft of said rotatablebrush, and an engaging portion engaged with said cam portion toreciprocate said non-rotational brush with rotation of said rotatablebrush.
 3. An apparatus according to claim 1, wherein said drivingmechanism includes a drive transmission mechanism for transmitting thedriving force of said driving source to said photosensitive member, anda driving connection mechanism for driving connection between saidphotosensitive member and said rotatable brush to rotate said rotatablebrush with rotation of said photosensitive member.